Method of improving the workability of a magnesium alloy extrusion



United States Patent 3,490,263 METHOD OF IMPROVING THE WORKABILITY OF A MAGNESIUM ALLOY EXTRUSION John F. Pashak, Linwood, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Oct. 2, 1967, Ser. N0. 671,933 Int. Cl. B21c 23/00, 23/14 US. Cl. 72256 8 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a novel method for improving the workability of a magnesium base alloy extrusion which comprises: providing a magnesium base alloy extrusion having a defined composition; working by rolling or drawing the extruded alloy in the same direction as the alloy was extruded to cause a reduction in the cross-sectional area of said extrusion, depending on the particular alloy, generally from about 0.5 to about 20 percent, thereby producing an improved magnesium base alloy extrusion.

Many magnesium base alloys are manufactured in extruded form, such as bars and rods, and later worked into the final product through a second mechanical operation. However, due to the hexagonal structure of magnesium base alloys, the initial extrusion operation causes the surface band of grains to have a highly preferred orientation. When the extruded-alloy is further worked to form the final product, surface cracks may appear due to the pro-- ferred orientation. This problem is particularly critical, e.g., with respect to the ASTM-designated magnesium base alloy, AZ2lXl, containing from 1.6 to 2.0 percent aluminum, .02 to .15 percent manganese, 1.0 to 1.4 percent zinc, .15 to .25 percent calcium, the balance being essentially magnesium when extruded into 0.4 to 1.25 inch diameter rods, cut into 0.3 to 1.2 inch pieces or slugs and impact extruded to form cans or containers for battery anodes. Apparently, because of the preferred orientation of the surface grains, cracking on the can surface occurs whenever the slug is placed in the impact extrusion machine with the nose or front (leading end) of the extruded slug facing the extrusion punch. Conversely, when the butt or trailing end of the extruded slug is placed facing the extrusion punch, essentially no cracks are present due to the twinning and recrystallization of the grains on impact. Thus the workability and use of AZZlXl, and possibly other extruded magnesium base alloys, has heretofore been limited apparently by the preferred orientation of the grains. Accordingly, it would be very desirable to provide a method avoiding the foregoing difficulties and improving the workability of magnesium base alloy extrusions with respect to subsequent or further working.

A primary object of the present invention is to provide a method for improving the subsequent workability of AZ21X1 extrusions.

Another object of the present invention is to provide a method for preparing AZ21X1 battery anodes as containers without surface cracks.

In accordance with the present invention the above and other objects and advantages are obtained in a novel method for improving the subsequent workability of magnesium base extrusions which comprises: providing a magnesium base alloy extrusion having the heretofore 3,490,263 Patented Jan. 20, 1970 ICC defined composition of AZ21X1; working said extrusion by rolling or drawing it in the same direction as extruded, reducing the cross-sectional area during the working of said extrusion from about 0.5 to about 20 percent, thereby producing an improved magnesium base alloy extrusion, which when subsequently fabricated as by impact extrusion avoids the cracking problem hereinbefore described.

Magnesium base alloy extrusions to be processed in accordance with the invention may be in rod, bar or other forms capable of being reduced in cross-sectional area within the limits of the reduction step of the present invention.

Surprisingly, rolling or drawing the extruded alloy in the same direction as the alloy was originally extruded so as to cause a reduction in cross-sectional area of from about 0.5 to about 20 percent eliminates the preferred orientation of the surface grains of the extruded alloy and improves the original magnesium base alloy extrusion with respect to subsequent working of same without cracks and defects. The rolling or drawing may be accomplished by conventional means, as practiced by those skilled in the art. For example, drawing may be done using a tapered drawing die with suitable lubricant at from about room temperature F.) to about 500 F. Rolling may also be accomplished at a temperature of from about 70 F. to about 500 F. Where reductions in area are less than about 1 percent, an annealing operation may be added to aid in the recrystallization of the surface grains, particularly at reductions of 0.5 to 0.7%.

The following examples are representative of the novel process of the present invention and are not intended to be construed as limiting the invention thereto.

EXAMPLES 1-20 The ASTM designated magnesium base alloy, AZ21X1, having a nominal composition of about 1.8 weight percent aluminum, about 0.08 weight percent manganese, about 1.2 weight percent zinc, about 0.2 weight percent calcium, the balance being essentially magnesium, was extruded at 600 F. and 800 F. into 1.25 inch diameter rod. After lubrication the nose or leading end of rod was positioned and adapted to fit in and through the tapered drawing die. Clamps on a drawing bench were then attached to the rod and the rod pulled through the die opening at room temperature thereby reducing the crosssectional area (percent RA) from about 0.5 to about 10.5 percent. In the same manner a rod of extruded AZ21X1 alloy pointed at the butt or back end was similarly drawn through the drawing die. For comparison purposes sample slugs of the AZ21X1 alloy were prepared in the extruded condition without drawing of any kind.

The drawn rods of extruded alloy were then cut into 0.66 inch slugs. The slugs were marked to identify the end nearest the nose, preheated at 600 F. for 5 minutes, and placed either butt up or nose up in an impact extrusion die preheated at 300 F. The die diameter was 1.256 inches; the punch diameter was 1.115 inches. The slugs were impact extruded to form battery anode cans or cups and inspected for surface cracking. Thus some slugs were drawn butt first and impacted butt first Column 1 of the table), some drawn butt first but impacted nose first (Column 2), some drawn nose first but impacted butt first (Column 3), and some dra'wn nose first and impacted nose first (Column 4). The number of cans cracked per number of cans impacted were recorded for each combination of drawing and extruding.

TABLE Cans cracked/cans impacted Drawing Drawn-butt first, Drawn-butt first, Drawn-nose first, Drawn-nose first Extrusion reduction, Anneal impactedbutt impacted-nose impacted-butt impacted-nose Example No. temp, F percent RA 1 lir., F. first first first first comparativesn 600 /5 5/5 D 800 0/ 5 5/5 600 0. 7 0/5 5/5 0/5 3/5 600 0. 7 0/5 5/5 0/5 0/5 800 0. 5 0/5 5/5 0/5 5/5 800 0. 5 0/5 5/5 0/5 0/5 600 2. 5 0/5 5/5 0/5 0/5 600 2. 5 0/5 5/5 0/5 0/5 800 2. 2 0/5 5/5 0/5 0/5 800 2.2 0/5 0/5 0/5 0/5 600 5. 6 0/5 5/5 0/5 0/5 600 5. 6 0/5 5/5 0/5 0/5 800 5.0 0/5 5/5 0/5 0/5 800 5. 0 0/5 3/5 0/5 0/5 600 7. 0 0/5 5/5 0/5 0/5 600 7. 0 0/5 5/5 0/5 0/5 800 7.0 0/5 5/5 0/5 0/5 800 7.0 0/5 5/5 0/5 O/5 800 9. 8 0/5 5/5 0/5 0/5 800 9. 8 0/5 5/5 0/5 0/5 600 10. 5 0/5 5/5 0/5 O/5 600 10. 5 0/5 2/5 0/5 015 The table shows that due to the preferred orientation of the surface grains, surface cracking occurred on the undrawn extruded cans and the cans drawn butt first whenever the rod was impacted nose first (Column 2). However, when the extruded rod was drawn through the tapered die nose first at reductions in area of from about 0.5 to about 10.5 percent little or no surface cracking occurred upon impact extrusion regardless of the direction of the impact extrusion (Columns 3 and 4). When lowreductions of drawing were used (Examples 14), a 700 F. anneal for one hour was used to aid in recrystallization of the surface grains. Thus drawing the extruded magnesium base alloy allowed the extruded alloy to be subsequently worked without concern for the direction of the original extrusion or surface cracking.

The present invention may be modified or changed without departing from the spirit or scope thereof and it is understood that the invention is only limited as defined in the appended claims.

I claim:

1. A method of improving the workability of a magnesium base alloy extrusion which comprises: providing a magnesium base alloy extrusion, wherein the magnesium base alloy consists essentially by weight of from about 1.6 to about 2.0 percent alumin um, about 0.02 to about 0.15 percent manganese, about 1.0 to about 1.4 percent zinc, and about 0.15 to about 0.25 percent calcium, the balance being essentially magnesium; working said extrusion by drawing or rolling in the same direction as the alloy was extruded, to cause an eifective reduction in cross-sectional area so as to effect a reorientation of the surface grains, thereby producing an improved magnesium base alloy extrusion.

2. The method of claim 1 wherein the reduction in cross-sectional area caused by drawing or rolling is 0.5 to percent.

3. The method of claim 1 wherein the working by drawing or rolling is carried out at from about 70 F. to about 500 F.

4. A method for preparing magnesium base alloy con:

tainers which comprises: extruding a magnesium base extruded, causing a reduction in crosssectional area of from about 0.5 to about 20 percent; cutting said drawn extruded rods into slugs; preheating said slugs; and impact extruding said slugs, thereby producing essentially crack-free magnesium base alloy containers.

5. The method of claim 4 wherein the drawing or rolling is carried out at from about 70 F. to about 500 F.

6. The method of claim 4 wherein the slugs are preheated at from about 400 F. to about 800 F. for about 20 seconds to about 30 minutes.

7. A method of improving the workability of a magnesium base alloy extrusion having surface grains with a preferred orientation which comprises: working said extrusion by drawing or rolling in the same direction as the alloy was extruded, to cause an effective reduction in cross-sectional area whereby reorientation of the surface grains is effected, thereby producing a magnesium base alloy extrusion with improved mechanical working properties.

8. A method which comprises: extruding a magnesium base alloy into a rod, said alloy in the extruded form characterized by surface grains with a preferred orientation; drawing or rolling said extruded rods in the same direction as extruded, causing a reduction in cross-sectional area of from about 0.5 to about 20 percent and a reorientation of the surface grains; cutting the drawn extruded rods into slugs; preheating said slugs; and impact extruding said slugs to produce an essentially crack free shaped product.

References Cited UNITED STATES PATENTS 1,902,905 3/ 1933 Schreiber 72-256 2,378,729 6/1945 Schmidt 72-700 3,125,222 3/1964 Foerster et al 72256 FOREIGN PATENTS 1,268,176 6/1961 France.

CHARLES W. LANHAM, Primary Examiner L. A. LARSON, Assistant Examiner US. Cl. X.R. 72-700 

